System of energy-efficient and constant-pressure parallel-coupled fluid-transport machines

ABSTRACT

The present invention discloses a system of energy-efficient and constant-pressure parallel-coupled fluid-transport machines, which can flexibly and massively provide gas and water to every fabrication unit. The system of the present invention comprises: variable-frequency centrifugal fluid-transport machines, pressure gauges, power meters, flow meters, and controllers. The performance curves of the abovementioned system of parallel-coupled fluid-transport machines and the system impedance curves of the loads are analyzed theoretically and built in the controllers together with the equal-efficiency curves provided by the manufacturer. When the system is operating, the data detected by the pressure gauges, power meters, and flow meters are compared with the built-in data to obtain the optimal energy-efficient conditions as the operational criteria of the system of the present invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a parallel-coupled fluid-transportmachinery, particularly to a system of energy-efficient andconstant-pressure parallel-coupled fluid-transport machines.

2. Description of the Related Art

For recent years, owing to the advance of technology, the industrialproducts are growing precise, delicate and miniature more and more. Tomass-produce those precise, delicate and miniature products in low cost,the current high-tech factories grow in scale continuously, and thequality requirements thereof also become more and more strict, which isa challenge for the building companies of the high-tech factory and thefacility engineers who maintain the high-tech factory, and which alsodrives the related personnel to zealously research solutions or developnew technologies to fulfill the requirements.

In the current high-tech factories, it is a basic requirement forfluid-transport machinery to supply the gas and water of sufficient flowrate and stable pressure to every unit requiring them. When the factoryis of smaller scale, merely a single fluid-transport machine is enoughto supply the required flow rate. When only a single machine is used,the pressure stability can be easily and simply controlled according theoperational manual provided by the manufacturer. However, in the currenthigh-tech factories, the scale of the factory is enlarged continuously,and the fabrication procedures also become more and more flexible, inorder to reduce the fabrication cost and to achieve the productdiversification, and therefore, a single-machine fluid-transport systemcan no more meet the requirement. In order to supply the gas and waterof sufficient flow rate and stable pressure to every unit requiring themand to shift the pressure and flow rate of gas and water as soon aspossible and meet the new procedure's requirements when the fabricationprocedures are changed, a system of multiple parallel-coupledfluid-transport machines is needed in the current high-tech factories.The operation of parallel-coupled fluid-transport machines is morecomplicated and crucial than that of a single fluid-transport machine,and just an imprudent operation may damage the machines. However, eventhe manufacturer cannot provide a standard operational procedure for thesystem of parallel-coupled transport-fluid transport machines. Thus, thefactory-building companies and the facility-maintaining personnel canonly depend on the experience accumulated in practical operation. Theoperational standard assumed in such a way is not only multitudinous andcomplicated but also neither analyzed theoretically nor verifiedexperimentally. Therefore, it is hard to determine whether the assumedoperational standard can achieve the required security and rapidity. Thesystem of multiple parallel-coupled fluid-transport machines consumesconsiderable energy; therefore, reducing the consumed energy thereof canbenefit the fabrication cost very much. However, the objective of savingenergy cannot be realized via the current operational standard, which isassumed from individual experience.

When the user purchases a centrifugal fluid-transport machine, such as apump, a blower, or an exhaust fan, the manufacturer will provide theuser with operational data, such as the performance curves shown inFIG. 1. In FIG. 1, the horizontal and vertical axes respectivelyrepresent flow rate and pressure. The performance curve of maximumusable rotation speed begins from the vertical axis and ends in somepoint of the diagram, which represents the critical usable point. Thearea located at the right side of the performance curve of maximumusable rotation speed is a region unsuitable to use. According theAffinity Law of fluid-transport machines, the relationships with respectto rotation speed (N), flow rate (Q), pressure (P), and power (HP) areshown below. $\begin{matrix}\left. \begin{matrix}{\frac{Q_{1}}{Q_{2}} = \frac{N_{1}}{N_{2}}} \\{\frac{H_{1}}{H_{2}} = \left( \frac{N_{1}}{N_{2}} \right)^{2}} \\{\frac{{HP}_{1}}{{HP}_{2}} = \left( \frac{N_{1}}{N_{2}} \right)^{3}}\end{matrix} \right\} & (1)\end{matrix}$

Based on the data of the performance curve of maximum usable rotationspeed, and via theoretical analysis and calculation, the followingequations respectively relating pressure (P) with rotation speed (N) andrelating pressure (P) with flow rate (Q) can be obtained.P=C ₁ N ² +C ₂ N+C ₃  (2)P=C ₁ Q ² +C ₂ Q+C ₃  (3)

Via equations (2) and (3), the performance curves of the rotation speedslower than the maximum usable speed can be obtained, as the dashedcurves shown in FIG. 1. Further, the equal-efficiency curves and theequal-power curves are also plotted in FIG. 1.

There are not many patents about the system of multiple parallel-coupledfluid-transport machines proposed before. The Taiwan Patent No. 506683“Parallel-coupled Electrical Fans” discloses: a system of multipleparallel-coupled electrical fans, wherein multiple electrical fans areinstalled in parallel to a one-piece frame; however, it does not mentionhow to control the parallel-coupled electrical fans at all. As to themethod of controlling the fluid-transport machine, the Taiwan Patent No.I225908 “Method of Controlling a Pump System” discloses: a method ofutilizing automatic control and operational parameters of a centrifugalpump to pump fluid to an outlet; however, this patent is confined to thecontrol of a single centrifugal pump, wherein pump rotation speed, watertemperature, pressures at the inlet and outlet of the pump, and thepressure difference thereof detected by the sensors are compared withthe pre-stored data, and then, the pump is adjusted according to thecomparing result. The Taiwan Patent No. M253699 “Devices of Controllinga Pump System” discloses: a variety of devices of controlling a singlecentrifugal pump, which is similar to the previous patent. As shown intheir claims, the abovementioned pre-stored data is not deduced from thetheories but acquired via arranging the data gathered from practicaloperations; such a method advantages in that the states of a pump, whichare to be the basis of control, can be easily and rapidly obtained;however, there are two constrains on such a method: one is that itcannot apply to the system of multiple parallel-coupled machines but canonly apply to a single machine; the other is that the control range islimited by the pre-stored data. About energy efficiency, whether energycan be saved thereby is an unknown.

Accordingly, via theoretical analysis and experimental verification, thepresent invention proposes a system of energy-efficient andconstant-pressure parallel-coupled fluid-transport machines and theoperational method thereof, which not only can achieve the secure,rapid, and energy-efficient operation of the system of multipleparallel-coupled fluid-transport machines but also can unify andsimplify the operational standard thereof, and the building cost thereofcan also be lowered.

SUMMARY OF THE INVENTION

Sequentially via the following theoretical analysis, equation deduction,and embodiment discussion, the system of energy-efficient andconstant-pressure parallel-coupled fluid-transport machines of thepresent invention will be described in detail below. The flow rate inthe load piping system is very important in the study of the system ofmultiple parallel-coupled fluid-transport machines; therefore, thedistribution of the flow rate in the load piping system is to becalculated firstly.

The piping system shown in FIG. 2 is to be used as an exemplification ofthe load piping of the system of multiple parallel-coupledfluid-transport machines. As shown in FIG. 2, the piping system has 9pipe sections (from pipe section 1 to pipe section 9) and 10 nodes (fromnode 1 to 10, including: fluid inlets, fluid outlets and confluencepoints, i.e. the ends of all the pipe sections). Nodes 1, 2, 5, 6 arethe inlets of branch pipes, and nodes 9, 10 are the total outlets. Pipesections 8, 9 respectively have fluid-transport machines, and the arrowsthereof are not necessarily the real flow direction but the assumptivedirection used in the calculation by programs. In the system, the valueto be calculated is the flow rate Q_(n) in each pipe section, whereinthe subscript n denotes the serial number of the pipe section. As thereare 9 pipe sections, there are nine unknown values Q₁, Q₂, - - - Q₉,which need nine independent linear equations to solve. According to theconservation of the flow rate at the nodes, the continuity equations canbe established; for example, at node 3, the flow rate in pipe section 3is equal to the sum of the flow rates in pipe sections 1 and 2, and itcan be mathematically expressed as equation (4):Q ₁ +Q ₂ −Q ₃=0   (4)Similarly, at nodes 4, 7, 8, there are also three flow-rate-conservationequations (5), (6), (7):Q ₃ +Q ₄ −Q ₅=0  (5)Q ₅ +Q ₆ −Q ₇=0  (6)Q ₇ +Q ₈ −Q ₉=0  (7)As the conservation of flow rate does not exist at nodes 1, 2, 5, 6, 9,and 10, there is no flow-rate-conversation equation to implement solvingflow rates.

The other five equations for solving flow rates can be acquired from theconservation of energy. For example, pipe section 3 has node 3 and node4 respectively at two ends thereof, and when the fluid flows from node 3to node 4, it means that the total pressure at node 3 is greater thanthat at node 4; the total pressures at nodes 3 and 4 are respectivelydenoted by P₃ and P₄; owing to friction and the piping structure, thereis a loss of total pressure when the fluid flows from node 3 to node 4;the total pressure loss is denoted by ΔP₃, and then,ΔP ₃ =P ₃ −P ₄  (8)The total pressure loss in pipe section 3 can also be mathematicallyexpressed as K₃Q₃ ² (it will be explained later), wherein K₃ is thecoefficient of the total pressure loss in pipe section 3; then, equation(8) can be written as:K ₃ Q ₃ ² =P ₃ −P ₄  (9)As each pipe section has its own structure and devices, each pipesection has different total pressure loss coefficient K_(n), wherein thesubscript is used to denote the serial number of the pipe section. Theleft portion of equation (9) has an unknown Q₃, and the right portionhas two unknowns P₃ and P₄; thus, increasing one equation is at the costof adding two redundant unknowns. The total pressures of all the inletsand outlets (i.e. nodes 1, 2, 5, 6, 9 and 10) can be supposed to beknown. When the fluid enters into the load piping from node 1 and flowsthrough pipe sections 1, 3, 5, 7 and 9 and then exits from 10, accordingto the principle of energy conservation, which has been used in equation(8),ΔP=P ₁ −P ₁₀  (10)wherein ΔP is the sum of the total pressure loss in every pipe sectionand the total pressure change caused by the fluid-transport machine.Thus,ΔP=ΔP ₁ +ΔP ₃ +ΔP ₅ +ΔP ₇ +ΔP ₉ −ΔP _(S9)  (11)wherein ΔP_(S9) is the total pressure change induced by thefluid-transport machine when the fluid flows through pipe section 9, andhow to deal with ΔP_(S9) will be discussed later. Substitute theexpression of ΔP in equation (11) for ΔP in equation (10), and rearrangethe terms as follows:ΔP _(S9) −ΔP ₉ −ΔP ₇ −ΔP ₅ −ΔP ₃ −ΔP ₁ =P ₁₀ −P ₁ =C ₁  (12)P₁₀ and P₁ are known and usually the pressures of the exteriorenvironments; therefore, C₁ is a constant. Transform ΔP into the form ofKQ² to obtain:ΔP _(S9) −K ₉ Q ₉ ² −K ₇ Q ₇ ² −K ₅ Q ₅ ² −K ₃ Q ₃ ² −K ₁ Q ₁ ² =C₁  (13)Similarly, the following equations can also be obtained:ΔP _(S9) −K ₉ Q ₉ ² −K ₇ Q ₇ ² −K ₅ Q ₅ ² −K ₃ Q ₃ ² −K ₂ Q ₂ ² =P ₁₀ −P₂ =C ₂  (14)ΔP _(S9) −K ₉ Q ₉ ² −K ₇ Q ₇ ² −K ₅ Q ₅ ² −K ₄ Q ₄ ² =P ₁₀ −P ₅ =C₃  (15)ΔP _(S9) −K ₉ Q ₉ ² −K ₇ Q ₇ ² −K ₆ Q ₆ ² =P ₁₀ −P ₆ =C ₄  (16)ΔP _(S8) −K ₈ Q ₈ ² −K ₇ Q ₇ ² −K ₆ Q ₆ ² =P ₉ −P ₆ =C ₅  (17)So far, from equations (4)˜(7) and from equations (13) to (17), thereare totally nine linear independent equations. In addition to nineunknowns of flow rates, there are still two unknowns ΔP_(S8) and ΔP_(S9)existing among those equations, which will be solved from theperformance curves of the fluid-transport machines.

The abovementioned quadratic polynomial equation (3) can match thereality very well; therefore, the performance curve of thefluid-transport machine at a given rotation speed can be mathematicallyexpressed as:ΔP _(S8) =C _(S1) Q ₈ ² +C _(S2) Q ₈ +C _(S3)  (18)ΔP _(S9) =C _(S1) ′Q ₉ ² +C _(S2) ′Q ₉ +C _(S3)′  (19)wherein C_(S1), C_(S2), C_(S3), C′_(S1), C′_(S2), and C′_(S3) are allconstants, and the subscript S denotes the fluid-transport machine.Except ΔP_(S8) and ΔP_(S9), each term in left sides of the equal signsof equations (13)˜(17) is the total pressure loss coefficient multipliedby the flow rate squared. In order to add ΔP_(S8) and ΔP_(S9) into thecalculation of the equations, via formula method, equations (18) and(19) are rewritten as:ΔP _(S8) =C _(S1) G ₈ ² +C _(S4)  (20)ΔP_(S9) =C _(S1) ′G ₉ ² +C _(S4)′  (21)wherein${G_{8} = {Q_{8} + \frac{C_{S\quad 2}}{2C_{S\quad 1}}}},{G_{9} = {Q_{9} + \frac{C_{S\quad 2}^{\prime}}{2C_{S\quad 1}^{\prime}}}},{C_{S\quad 4} = {C_{S\quad 3} - \frac{C_{S\quad 2}^{2}}{4C_{S\quad 1}}}},{and}$$C_{S\quad 4}^{\prime} = {C_{S\quad 3}^{\prime} - \frac{C_{S\quad 2}^{2\prime}}{4C_{S\quad 1}^{\prime}}}$Substitute the expression of ΔP_(S9) in equation (21) for ΔP_(S9) inequation (13), and rearrange the terms as follows:C _(S1) ′G ₉ ² −K ₉ Q ₉ ² −K ₇ Q ₇ ² −K ₅ Q ₅ ² −K ₃ Q ₃ ² −K ₁ Q ₁ ² =C₁ −C _(S4)′  (22)

Similarly, the expression of ΔP_(S8) and ΔP_(S9) in equations (20) and(21) can also substitute for ΔP_(S8) and ΔP_(S9) in equations (14)˜(17).It can be found: in addition to the unknowns of flow rates, there arestill two unknowns G₈ and G₉ existing in the left sides of the equalsigns, and therefore, further two equations are needed, i.e. increasingone fluid-transport machine will increase one unknown also. From theprocess of the formula method, the relationships of G₈ and G₉ versus theflow rates of the corresponding pipe sections can be derived andmathematically expressed as: $\begin{matrix}{{G_{8} - Q_{8}} = \frac{C_{S\quad 2}}{2C_{S\quad 1}}} & (23) \\{{G_{9} - Q_{9}} = \frac{C_{S\quad 2}^{\prime}}{2C_{S\quad 1}^{\prime}}} & (24)\end{matrix}$So far, the system of equations has 11 equations and 11 unknowns, andthus, the flow rates of all the pipe sections can be solved. The K_(n)(n=1, 2, . . . , 9) in equations (13)˜(17) are all known values, andthey are the coefficients of the total pressure loss, which includes:the loss caused by the friction between the fluid and the pipe, and theminor loss caused by the devices and parts installed to the pipe;therefore, the K values can be obtained via referring to the pipe losscoefficients.

When the fluid-transport machines of the same specification are coupledin parallel, the flow rate in the performance curve will also increaseas many times as the fluid-transport machine does. FIG. 3 shows theperformance curves of the systems having different numbers ofparallel-coupled fluid-transport machines operating at a fixed speed. Asshown in FIG. 3, at an identical pressure, the flow rate provided by twoparallel-coupled fluid-transport machines is the double of that providedby a single fluid-transport machine. Similarly, at an identicalpressure, the flow rate provided by three parallel-coupledfluid-transport machines is the triple of that provided by a singlefluid-transport machine. In other words, the performance curves changewith the quantities of parallel-coupled fluid-transport machines. If theperformance curve of a single fluid-transport machine is mathematicallyexpressed as:P=C _(S1) Q ² +C _(S2) Q+C _(S3)  (25)wherein C_(S1), C_(S2), and C_(S3) are constants. Let Q_(n) (n=1, 2, 3,. . . , n) denote the integrated flow rate of the system of theparallel-coupled fluid-transport machines with n denoting the number ofthe parallel-coupled fluid-transport machines. When n fluid-transportmachines are coupled in parallel, the fluid rate thereof will increaseby n times, i.e. Q_(n)=n·Q ; substitute it into equation (25) to obtainthe following equation: $\begin{matrix}{P = {{\frac{C_{S\quad 1}}{n^{2}}Q_{n}^{2}} + {\frac{C_{S\quad 2}}{n}Q_{n}} + C_{S\quad 3}}} & (26)\end{matrix}$which mathematically expresses the performance curve of the singleequivalent machine of the system of multiple parallel-coupledfluid-transport machines.

For a complicated piping system, if the setting of the system isunchanged, the total pressure loss of the system will be proportional tothe total flow rate squared. A system impedance curve can be formed viaplotting the total pressure loss P against the total flow rate Q and canbe mathematically expressed as:ΔP _(sys) =K _(sys) Q _(sys) ²  (27)wherein K_(sys) is a constant, and Q_(sys) is the total flow rate of thesystem, and ΔP_(sys) is the total pressure loss of the system.Therefore, with the system conditions unchanged, if the pressures atsome flow rates are known, the system impedance curve can be acquiredthereby.

FIG. 4 shows a system impedance curve and a performance curve of asingle fluid-transport machine and an intercept point of them. Thepressure and the flow rate corresponding to the intercept point areexactly the total pressure loss and the total flow rate of the systemrespectively, and therefore, the intercept point is called theoperational point. In the piping system of a single fluid-transportmachine, the total pressure loss of the system is equal to the pressureprovided by the fluid-transport machine, and the total flow rate of thesystem is equal to the flow rate of the fluid-transport machine. If themathematic expressions of the performance curve of the fluid-transportmachine and the system impedance curve are known, substitute equation(27) into the equation of the performance curve to obtain:C _(S1) Q _(sys) ² +C _(S2) Q _(sys) +C _(S3) =K _(sys) Q _(sys) ²  (28)and then, obtain the solutions of Q_(sys)—the flow rate at the interceptpoint (the operational point) of the those two curves—via the formulamethod: $\begin{matrix}{Q_{sys} = \frac{{- C_{S\quad 2}} \pm \sqrt{C_{S\quad 2} - {4\left( {C_{S\quad 1} - K_{sys}} \right)C_{S\quad 3}}}}{2\left( {C_{S\quad 1} - K_{sys}} \right)}} & (29)\end{matrix}$

For a fluid-transport machine installed in a piping system and operatingat a fixed rotation speed, the flow rate thereof can be solved fromequation (29). If the solved flow rate is not the expected value, theflow rate can be adjusted via changing the rotation speed of thefluid-transport machine. When the rotation speed of the fluid-transportmachine is changed, the performance curve thereof also changes, and theoperational point too. The performance curve of the fluid-transportmachine can be worked out via the calculation according to the AffinityLaw, and the relationships of flow rate versus rotation speed, pressureversus rotation speed, and power versus rotation speed have been shownin equation (1).

FIG. 5 shows the performance curves of a fluid-transport machine when itoperates at the rotation speeds of 1750 rpm and 2275 rpm, wherein PointA and Point B are the operational points for different rotation speedsin the fixed system. From equation (27), the following relationship canbe obtained: $\begin{matrix}{\frac{P_{A}}{P_{B}} = {\frac{K_{sys}Q_{A}^{2}}{K_{sys}Q_{B}^{2}} = \frac{Q_{A}^{2}}{Q_{B}^{2}}}} & (30)\end{matrix}$According to equation (1), the relationship between Point A in theperformance curve of 1750 rpm and Point C in the performance curve of2275 rpm can be written as: $\begin{matrix}{\frac{Q_{A}}{Q_{C}} = \frac{N_{1750}}{N_{2275}}} & (31) \\{\frac{P_{A}}{P_{C}} = \frac{N_{1750}^{2}}{N_{2275}^{2}}} & (32)\end{matrix}$Substituting equation (31) into equation (32) can obtain:$\begin{matrix}{\frac{P_{A}}{P_{C}} = \frac{Q_{A}^{2}}{Q_{C}^{2}}} & (33)\end{matrix}$Via comparing equation (30) and equation (33), it is found: that Point Bis exactly Point C. Therefore, when Operational Point A is known,Operational Point B, i.e. the intercept point of another performancecurve and the system impedance curve, can be worked out with theAffinity Law.

When the pressure and the flow rate of Point B is the target pressureand the target flow rate of the system yet with the rotation speed ofthe fluid-transport machine being unknown, the rotation speed can beworked out as follows:Firstly, according to equation (27), the parameter K_(sys) is obtainedby: $\begin{matrix}{K_{sys} = \frac{P_{B}}{Q_{B}^{2}}} & (34)\end{matrix}$Suppose that the performance curve of the fluid-transport machineoperating at the rotation speed of 1750 rpm can be mathematicallyexpressed as equation (25). Substitute the coefficients of equation (25)and equation (34) into equation (29) to obtain the flow rate of thesystem Q_(A).Then, according to equation (1), the rotation speed can be obtained by:$\begin{matrix}{N_{sys} = {N_{1750}\frac{Q_{B}}{Q_{A}}}} & (35)\end{matrix}$Thus, the target flow rate can be obtained via adjusting the rotationspeed of the fluid-transport machine to N_(sys). According to equation(1), the performance curve of the adjusted rotation speed can bemathematically expressed as: $\begin{matrix}{{\frac{N_{1750}^{2}}{N_{sys}^{2}}P} = {{C_{S\quad 1}\left( {\frac{N_{1750}}{N_{sys}}Q} \right)}^{2} + {C_{S\quad 2}\left( {\frac{N_{1750}}{N_{sys}}Q} \right)} + C_{S\quad 3}}} & (36)\end{matrix}$Rearrange it to obtain: $\begin{matrix}{P = {{C_{S\quad 1}Q^{2}} + {C_{S\quad 2}\frac{N_{sys}}{N_{1750}}Q} + {\frac{N_{sys}^{2}}{N_{1750}^{2}}C_{S\quad 3}}}} & (37)\end{matrix}$

According to the principles mentioned above, and based on the data shownin FIG. 6 and FIG. 7, the performance curve of FIG. 8 can bemathematically expressed as:P=−0.8889Q ²+6.6667Q+700  (38)In this exemplification, three fluid-transport machines of the samespecification are coupled in parallel. According to equation (26), theperformance curve of the single equivalent fluid-transport machine canbe mathematically expressed as:P=−0.0988Q ²+2.2222Q+700  (39)Via equation (27), K_(sys) is obtained by: $\begin{matrix}{K_{sys} = {\frac{563}{40^{2}} = 0.352}} & (40)\end{matrix}$Substitute the coefficients of the equation (39) and the constant ofequation (40) into equation (29) to obtain:$Q_{sys} = {\frac{{- 2.2222} - \sqrt{2.2222 - {4\left( {{- 0.0988} - 0.352} \right)700}}}{2\left( {{- 0.0988} - 0.352} \right)} = {41.9{({cfs}).}}}$AS shown in FIG. 9, the worked-out total flow rate of the system is 41.9cfs; however, the total flow rate required by the system is only 40 cfs;therefore, the rotation speed of the fluid-transport machine should belowered. Suppose equation (38) is of the performance curve of therotation speed of 1750 rpm. The desired rotation speed can be obtainedaccording to equation (35) by:$N_{sys} = {{N_{1750}\frac{Q_{B}}{Q_{A}}} = {{1750\frac{40}{41.9}} \approx {1670{({rpm}).}}}}$When the rotation speed is reduced to 1670 rpm, the performance curvecan be obtained according to equation (37) and mathematically expressedas:P=−0.8889Q²+6.3619Q+637.46  (41)

Adopt the performance curve mathematically expressed by equation (41);the recalculated total flow rate will be 40 cfs, and the flow rates ofall outlets are almost identical, and the pressures thereof are alsouniform, as shown in the portion for three parallel-coupled machines ofFIG. 10. According to the same method, the rotation speed required bytwo parallel-coupled machines can also be worked out, and the rotationspeed thereof should be raised to 1850 rpm. As shown in the portion fortwo parallel-coupled machines of FIG. 10, the flow rates of all outletsare also almost identical, and the errors of the pressures are withinonly 2%.

As to the equal-efficiency curves in FIG. 1, they cannot be deducedtheoretically but are obtained experimentally form practical operationby the manufacturer, and those data is no more further analyzed but willbe used directly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the data of a centrifugal fluid-transportmachine.

FIG. 2 is a diagram showing the system of multiple parallel-coupledfluid-transport machines and the load piping system.

FIG. 3 is a diagram showing the performance curves of a singlefluid-transport machine, the system of two parallel-coupledfluid-transport machines, and the system of three parallel-coupledfluid-transport machines.

FIG. 4 is a diagram showing the performance curve of a fluid-transportmachine and the system impedance curve.

FIG. 5 is a diagram showing the performance curves of a fluid-transportmachine operating at the rotation speeds of 1750 rpm and 2275 rpm.

FIG. 6 is a diagram showing the structure of a load piping system.

FIG. 7 is a diagram showing the data of a working fluid and the data ofall pipe sections.

FIG. 8 is a diagram showing the performance curves of a fluid-transportmachine operating at the rotation speed of 1750 rpm.

FIG. 9 is a diagram showing the flow rate distribution in each of theoutlets when the fluid-transport machines operate at the rotation speedof 1750 rpm.

FIG. 10 is a diagram showing the flow rate distribution in each of theoutlets when the fluid-transport machines operate at the rotation speedof 1670 rpm.

FIG. 11 is a diagram showing the flow rate and the pressure required bythe system and the performance curves of the system of twoparallel-coupled fluid-transport machines and the system of threeparallel-coupled fluid-transport machines.

FIG. 12 is a diagram showing the performance curves of the system of twoparallel-coupled fluid-transport machines and the system of threeparallel-coupled fluid-transport machines.

FIG. 13 is a diagram showing the data relating to pressure and flow rateand containing equal-efficiency curves

FIG. 14 is a diagram showing the convention operational method and theoperational method of the present invention.

FIG. 15 is a diagram showing the layout of the constituent parts of thepresent invention.

FIG. 16 is a diagram showing the architecture of the system control.

DETAILED DESCRIPTION OF THE INVENTION

In practical operation, the time allowed to determine operationalparameters is very short; therefore, it is hard to utilize the equationsdeduced above to calculate the operational parameters and then apply theworked-out parameters to control the system; thus, the requiredoperational parameters are worked out beforehand, and then, the work-outparameters are directly applied to the system. The embodiments describedbelow are to exemplify that the results worked out via theabovementioned equations are directly applied to the practical cases.

The embodiment to be discussed below supposes that the flow raterequired by the system is Q_(T), and the pressure of the system is aconstant pressure P_(T), and the maximum flow rate a single pump canprovides is Q₁, and the maximum pressure a single pump can provide isP₁. When the system uses multiple pumps, the embodiment also supposesthat those pumps are of the same specification of the same manufacturerin principle. From the abovementioned basic data, it is known: ifQ_(T)>Q₁, a single pump cannot meet the requirement of flow rate, and ifP₁>P_(T), it can meet the requirement of pressure.

In the conventional operational method, the system impedance can becalculated from the piping layout and the flow rate of each pipesection, and the system impedance curve can be formed via plotting thesystem impedance against the flow rate, and the conventional operationalmethod comprises the following procedures:

-   (1) Turn on a first pump; however, as shown in FIG. 11, the    performance curve of the single pump (the solid curve) cannot    intercept the system impedance curve at Operational Point O of    P=P_(T) and Q=Q_(T);-   (2) Turn on a second pump with the operational conditions the same    as that of the first pump; the performance curve of two    parallel-coupled pumps (- - -) intercepts the system impedance curve    at Point X, which exceeds the system requirement; then, the rotation    speeds of those two pumps are lowered, and thus, the performance    curve of two parallel-coupled pumps (-{dot over ( )}-) can intercept    the system impedance curve at Operational Point O;-   (3) If a third pump is also turned on, as shown in FIG. 12, via    appropriately adjusting the rotation speed of each pump similar to    that used in the case of two parallel-coupled pumps, the performance    curve of three parallel-coupled pumps can also intercept the system    impedance curve at Operational Point O;-   (4) Keep on increasing the number of operating pumps, via    appropriately adjusting the rotation speed of each pump similarly,    the performance curve of multiple parallel-coupled pumps can also    intercept the system impedance curve at Operational Point O;-   (5) Thus, the system requirement can be satisfied with only two    parallel-coupled pumps or more.

However, the conventional operational method leaves the followingproblems to be solved: how many pumps should be parallel coupled so thatthe system can be the most energy-efficient, and how to adjust thenumber of parallel-coupled pumps to achieve the optimal state when thesystem impedance curve is changed by the change of the required flowrate, which are also the subjects the present invention desires toovercome.

From the pump theory, it is known: when the output flow rate of eachpump is the same, energy saving is more likely to achieve. For example,the case of Q₁=Q₂=Q₃ is more energy-efficient that the case of Q₁≠Q₂≠Q₃.Therefore, making the flow rate output by each pump be equal will be thefirst task intended to do.

To enable the flow rate of each pump to be equal, power meters arerespectively installed to all the pumps, and according to the valuesdetected by the power meters, the flow rate of each pump can be obtainedby: $\begin{matrix}{{H\quad P} = \frac{P \times Q}{constant}} & (42)\end{matrix}$wherein P is the system pressure and maintained unchanged; the constantis the product of the pump efficiency and the unit conversion factor.The efficiency should be identical when the states of all the pumps arethe same. Once the power is known, the flow rate will be known also. Inother words, if the power of each pump is identical, i.e. HP₁=HP₂=HP₃,Q₁=Q₂=Q₃ . Flow meters can also be installed to the pumps, and the flowrate can be directly detected; however, the error of the flow meter isgreat, and the response thereof is also slow; therefore, using powermeters is a more suitable measure.

The abovementioned method can achieve a better energy-efficient effectwhen multiple pumps are coupled in parallel, but it cannot determine howmany pumps should be parallel coupled to achieve the bestenergy-efficient effect yet; for example, it cannot determine which oneof Q₁=Q₂=Q₃ and Q₁=Q₂ is better.

FIG. 12 shows the performance curve of two parallel-coupled pumps andthe performance curve of one of those two parallel-coupled pumps,wherein via flow meters, those two pumps are adjusted so that$Q_{1} = {Q_{2} = \frac{Q_{T}}{2}}$and P₁=P₂=P_(T). The dashed curve is the performance curve of twoparallel-coupled pumps, and appropriately adjusting the rotation speedof each pump can enable the performance curve of two parallel-coupledpumps to intercept the system impedance curve at Operational Point O.The solid curve is the performance curve of one of those twoparallel-coupled pumps, and Point O₂ thereof has the flow rate ofQ_(T)/2 and the pressure of P_(T). FIG. 12 also shows the performancecurve 2 of three parallel-coupled pumps and the performance curve of oneof those three parallel-coupled pumps, wherein via flow meters, thosethree pumps are adjusted so that$Q_{1} = {Q_{2} = {Q_{3} = {\frac{1}{3}Q_{T}}}}$and P₁=P₂=P₃=P_(T). The dot-dashed curve is the performance curve ofthree parallel-coupled pumps, and similarly, appropriately adjusting therotation speed of each pump can enable the performance curve of threeparallel-coupled pumps to intercept the system impedance curve atOperational Point O. The performance curve of one of those threeparallel-coupled pumps is denoted by the other solid curve, and Point O₃thereof has the flow rate of $\frac{1}{3}Q_{T}$and the pressure of P_(T). Both the measure of two parallel-coupledpumps and the measure of three parallel-coupled pumps can achieve thepressure P_(T) and the flow rate Q_(T) required by the system. Thepressures provided by the pumps of both the measures are all equal toP_(T); however, the flow rates provided by the pumps of both themeasures are respectively Q_(T)/2 and Q_(T)/3, and Point O₂ is differentfrom Point O₃.

As mentioned above, the manufacturer provides the equal-efficiencycurves for each specification of pump. Plotting the equal-efficiencycurves on FIG. 12 will obtain FIG. 13. The hyperbolic dashed curves onFIG. 13 are respectively the equal-efficiency curves of 70% efficiency(η), 60% efficiency (η) and 50% efficiency (η), which are plotteddirectly from the data provided by the manufacturer, and the bottompoints thereof are interconnected to form a dot-dashed curve. As thereis the constraint of constant pressure P_(T), Point O₂, Point O₃, andPoint O are all on the same horizontal line. In FIG. 13, Point O₂ is onthe equal-efficiency curve of 60% efficiency (η), and Point O₃ is on theequal-efficiency curve of about 65% efficiency (η). The total outputpower of the parallel-coupled pumps (HP)_(T) is the product of(HP)_(SINGLE PUMP) and the number n of parallel-coupled pumps:$\begin{matrix}{{\left( {H\quad P} \right)_{T} = {H\quad P_{{SINGLE}\quad{PUMP}} \times {the}\quad{number}\quad{of}\quad{pumps}\quad(n)}}{wherein}} & (43) \\{{\left( {H\quad P} \right)_{{SINGLE}\quad{PUMP}} = \frac{P_{T} \times Q}{{constant} \times {\eta(\%)}}}{{Thus},}} & (44) \\{\left( {H\quad P} \right)_{T\quad 2} = {{\frac{P_{T} \times \frac{1}{2}Q_{T}}{{constant} \times \left( {60\%} \right)} \times 2} = \frac{P_{T} \times Q_{T}}{{constant} \times \left( {60\%} \right)}}} & (45) \\{\left( {H\quad P} \right)_{T\quad 3} = {{\frac{P_{T} \times \frac{1}{3}Q_{T}}{{constant} \times \left( {65\%} \right)} \times 3} = \frac{P_{T} \times Q_{T}}{{constant} \times \left( {65\%} \right)}}} & (46)\end{matrix}$From equations (45) and (46), it is known: (HP)_(T3) is smaller than(HP)_(T2), i.e. the total output power of three parallel-coupled pumpsis smaller than that of two parallel-coupled pumps; in other words, thesystem of three parallel-coupled pumps is more energy-efficient than thesystem of two parallel-coupled pumps.

When the system flow rate is changed to meet the requirement offabrication, the system impedance curve will also change. When the flowrate increases, the system impedance curve will shift right, and whenthe flow rate decreases, the system impedance curve will shift left.When the flow rate increases, there are two measures to deal with it:(1) do not increase the number of pumps but raise the rotation speed ofthe existing pumps, (2) do not raise the rotation speed of the pumps butincrease the number of pumps (In this case, the rotation speed may evenneed to decrease). According to the abovementioned principles, the totalpowers of those two measures can be respectively worked out to determinewhich measure has smaller power consumption and then determine whichmeasure is to be adopted. When the flow rate decreases, there are alsotwo measures to deal with it: (1) do not decrease the number of pumpsbut lower the rotation speed of the existing pumps, (2) do not lower therotation speed of the pumps but decrease the number of pumps (In thiscase, the rotation speed may even need to increase). Similarly, thetotal powers of those two measures can be respectively worked out todetermine which measure has smaller power consumption, and which measureis to be chosen depends on which measure consumes less power.

When the system impedance curve is changed, decreasing, increasing, ormaintaining the number of pumps needs an operation action to change therotation speeds of the pumps, which is very critical to the high-techfactory. It is well known: high-tech factories take maintaining thestability of operational environment very seriously; inappropriatechange of operational environment will endanger the fabricatingproducts. It is often reported by the news: a short instability of powersupply instantly harms local manufacturers and causes considerable loss.According to the principle of the performance curve, when the rotationspeed of pumps is changed, the pressure of fluid supply would be changedalso. Similar to the change of power supply voltage, the change ofpressure also has a profound influence. Just a slight imprudence maycause a serious damage. For the current system, the time allowed toadjust the system is very short; further, after the pressure is changed,the system requires response time to resume the stability of pressure.In the conventional operational method, when the system needs toincrease flow rate, the rotation speed is often firstly raised sosteeply that the pressure is found exceeding the set pressure very soon;then, the rotation speed is reduced so steeply that the pressure isfound lower than the set pressure very soon again; then, the rotationspeed is raised once more. After a period of repeating theabovementioned process, the system finally assumes a stable pressureperformance at the set pressure. The relationship of pressure (P) versustime (T) of the abovementioned process is shown by the dashed curve ofFIG. 14.

Pressure is the driving force of fluid. The inappropriate change ofpressure will cause the sudden change of the flow rate supply at theoutlets, which will certainly bring about damage on the products andalways besets the manufacturers, the operators and the maintenancepersonnel. In the conventional technologies, when the requirement offlow rate is decreased, how to lower the rotation speed of pumps or howmany pumps is to be turned off is an unknown; therefore, the measure todeal with the change is often not to change, i.e. the operationalconditions is maintained unchanged, but the surplus fluid is recycled.It is obviously spending precious energy in vain.

Accordingly, the present invention proposes a scheme to rapidly andenergy-efficiently deal with the abovementioned flow rate change. Fromthose discussed above, it is known: when the system impedance curve ischanged (i.e., the required flow rate is changed), the system and methodproposed by the present invention can quickly work out the optimalnumber of operating pumps and the optimal rotation speed thereof. Thus,the rotation speed of pumps will be adjusted to be slightly less thanthe optimal rotation speed. When the pressure change is confirmed, thepumps will be slightly adjusted once more to operate at the optimalrotation speed. The relationship of pressure (P) versus time (T) of theabovementioned process is shown by the solid curve of FIG. 14. Thereby,the fluid pressure of the system will not rise and fall repeatedly, andthe flow supply at the outlets will no more increase and decreasealternately. Therefore, the present invention advantages the qualitystability very much.

According to the embodiments of the present invention, the system ofenergy-efficient and constant-pressure parallel-coupled fluid-transportmachines of the present invention comprises: multiple variable-frequencycentrifugal fluid-transport machines (61), multiple power meters (62),multiple pressure gauges (63), multiple flow meters (64), multiplecontrollers (65) and a load piping system (66), as shown in FIG. 15. Thefunctions of those constituent parts, the interactions thereof and thecontrol procedures are shown in FIG. 16 a diagram showing the controlarchitecture of the system of the present invention.

In conclusion, the present invention proposes a system ofenergy-efficient and constant-pressure parallel-coupled fluid-transportmachines, wherein the data required by the parallel-coupledfluid-transport machines is worked out via theoretical analysis andequation deduction; the worked-out data is used to control the system ofparallel-coupled fluid-transport machines so that the system operationcan be secure and quick. Further, the present invention can work out theoutput powers of the system of different numbers of parallel-coupledfluid-transport machines and then can determine the number of operatingfluid-transport machines, which can achieve the best energy-efficientperformance according to the output powers thereof. The presentinvention is distinct from the abovementioned published patents;therefore, the novelty and non-obviousness of the present invention isdoubtless.

What is claimed is:
 1. A system of energy-efficient andconstant-pressure parallel-coupled fluid-transport machines, comprising:performance curves of said system of energy-efficient andconstant-pressure parallel-coupled fluid-transport machines, systemimpedance curves of loads, equal-efficiency curves, and multiple branchpiping systems coupled in parallel, wherein each said parallel-coupledbranch piping system further comprises: a variable-frequency centrifugalfluid-transport machine, power meters, pressure gauges, flow meters, anda controller.
 2. The system of energy-efficient and constant-pressureparallel-coupled fluid-transport machines according to claim 1, whereinsaid performance curves of said system of energy-efficient andconstant-pressure parallel-coupled fluid-transport machines are workedout according to the relationships of the flow rate and the pressure ofsaid parallel-coupled fluid-transport machine.
 3. The system ofenergy-efficient and constant-pressure parallel-coupled fluid-transportmachines according to claim 1, wherein said system impedance curves ofloads are worked out with the relationships of the flow rate and theimpedance deduced from the load piping layout.
 4. The system ofenergy-efficient and constant-pressure parallel-coupled fluid-transportmachines according to claim 1, wherein said equal-efficiency curves arederived from the data provided by the manufacturer and stored in theform of a database containing the function relationships between flowrate and pressure.
 5. The system of energy-efficient andconstant-pressure parallel-coupled fluid-transport machines according toclaim 1, wherein said variable-frequency centrifugal fluid-transportmachines are formed of variable-frequency centrifugal pumps.
 6. Thesystem of energy-efficient and constant-pressure parallel-coupledfluid-transport machines according to claim 1, wherein saidvariable-frequency centrifugal fluid-transport machines are formed ofvariable-frequency centrifugal blowers.
 7. The system ofenergy-efficient and constant-pressure parallel-coupled fluid-transportmachines according to claim 1, wherein said variable-frequencycentrifugal fluid-transport machines are formed of variable-frequencycentrifugal exhaust fans.
 8. The system of energy-efficient andconstant-pressure parallel-coupled fluid-transport machines according toclaim 1, wherein said pressure gauges are used to detect the pressure offluid-transport pipes in order to maintain the state of constantpressure.
 9. The system of energy-efficient and constant-pressureparallel-coupled fluid-transport machines according to claim 1, whereinsaid power meters are used to measure the power output by saidvariable-frequency centrifugal fluid-transport machines, and the flowrate can be obtained via substituting the measured power into theequation: flow rate=(power×constant)/(pressure), and said constant is aunit conversion factor.
 10. The system of energy-efficient andconstant-pressure parallel-coupled fluid-transport machines according toclaim 1, wherein said flow meters are used to measure the flow rateoutput by said variable-frequency centrifugal fluid-transport machinesin order to guarantee that each said machine output an identical flowrate.
 11. The system of energy-efficient and constant-pressureparallel-coupled fluid-transport machines according to claim 2, whereinsaid controller is formed of a programmable logic controller and hasbuilt-in data of said performance curves of said system ofenergy-efficient and constant-pressure parallel-coupled fluid-transportmachines in order to execute related calculation.
 12. The system ofenergy-efficient and constant-pressure parallel-coupled fluid-transportmachines according to claim 3, wherein said controller is formed of aprogrammable logic controller and has built-in data of said systemimpedance curves of loads in order to execute related calculation. 13.The system of energy-efficient and constant-pressure parallel-coupledfluid-transport machines according to claim 4, wherein said controlleris formed of a programmable logic controller and has built-in data ofsaid equal-efficiency curves in order to execute related calculation.14. The system of energy-efficient and constant-pressureparallel-coupled fluid-transport machines according to claim 2, whereinsaid controller is formed of a computer and has built-in data of saidperformance curves of said system of energy-efficient andconstant-pressure parallel-coupled fluid-transport machines in order toexecute related calculation.
 15. The system of energy-efficient andconstant-pressure parallel-coupled fluid-transport machines according toclaim 3, wherein said controller is formed of a computer and hasbuilt-in data of said system impedance curves of loads in order toexecute related calculation.
 16. The system of energy-efficient andconstant-pressure parallel-coupled fluid-transport machines according toclaim 4, wherein said controller is formed of a computer and hasbuilt-in data of said equal-efficiency curves in order to executerelated calculation.
 17. The system of energy-efficient andconstant-pressure parallel-coupled fluid-transport machines according toclaim 11, wherein according to calculation results, said programmablelogic controller controls the rotation speed of a variable-frequencycentrifugal fluid-transport pump, or a variable-frequency centrifugalfluid-transport blower, or a variable-frequency centrifugalfluid-transport exhaust fan.
 18. The system of energy-efficient andconstant-pressure parallel-coupled fluid-transport machines according toclaim 14, wherein according to calculation results, said computercontrols the rotation speed of a variable-frequency centrifugalfluid-transport pump, or a variable-frequency centrifugalfluid-transport blower, or a variable-frequency centrifugalfluid-transport exhaust fan.